Recently, the use of optical discs such as compact discs and laser discs have been greatly increased. In the future, these optical discs will be used in all technical fields, by virtue of their advantages of a capability of storing a lot of information and convenience of use.
However, optical discs require an optical pick-up device for reading information recorded thereon.
Moreover, optical devices which have been generally used for reading information recorded on optical discs are very sensitive to vibration. As a result, it is very difficult to read accurately information recorded on optical discs at places where severe vibrations occur.
Referring to FIG. 1, there is illustrated a general optical pick-up device. As shown in FIG. 1, the optical pick-up device comprises a semiconductor laser diode 21 as a light source, a half mirror 22 positioned downstream of the laser diode 21 and adapted to reflect light beams emitted from the laser diode 21 at a predetermined angle, and a 45.degree. mirror 23 positioned downstream of the half mirror 22 and adapted to reflect the light beams reflected from the half mirror 22 at an angle of 45.degree.. Positioned downstream of the 45.degree. mirror 23 is a focusing lens 24 which feeds the light beams reflected from the 45.degree. mirror 23 to an optical disc 25 so that information recorded on the optical disc 25 can be read. The optical pick-up device also comprises a condensing lens 26 positioned at a path along which light beams reflected from the optical disc 25 is reflected. The condensing lens 26 is adapted to condense the light beams reflected from the optical disc 25. Downstream of the condensing lens 26, a photodetector 27 is also positioned, so as to sense light beams condensed by the condensing lens 26.
Operation of the optical pick-up device with the above-mentioned arrangement will now be described.
First, light beams emitted from the laser diode 21 is reflected by the half mirror 22 so that they are fed to the 45.degree. mirror 23. The light beams fed to the 45.degree. mirror 23 are then reflected by the 45.degree. mirror 23 at an angle of 45.degree., so as to be fed to the focusing lens 24. The focusing lens 24 focuses the light beams incident thereon and then transmits them to the optical disc 25. The light beams incident on the optical disc 25 are then reflected with different reflection amounts, according to forms of information recorded on the optical disc 25.
The light beams reflected from the optical disc 25 are fed to the focusing lens 24 which, in turn, converts them into parallel light beams. The parallel light beams are then fed to the condensing lens 26, so as to be condensed. The condensed light beams are detected by the photodetector 27. The light beams reflected by the optical disc 21 have different intensities, according to information recorded on the optical disc 21. By virtue of such a difference in light amount, the recorded information can be read.
However, such a general optical pick-up device has a bulky optical system, since elements thereof should be arranged at individual positions. As a result, there is a difficulty in applying such an optical pick-up device to appliances which are on a compacting trend. Moreover, the assembling of elements at their individual positions results in a lengthened adjusting time and a poor ability in assembling. Consequently, the manufacture cost and the poor product rate are increased.